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System Description
•
Supports in-band Diagnostic Communication Channel (DCC) with remote SC 553 DSUs for
configuration, alarms, diagnostics; DCC also supports firmware download and Telnet terminal
interface.
•
Allows the linking of FT1 services with traditional Dataphone Digital Service (DDS) and
generic digital services.
•
Supports both Alternate Mark Inversion (AMI) and Bipolar with 8 Zero Substitution (B8ZS)
line codes, and allows a variety of options for ones density in the data stream.
•
Supports both AT&T TR-54016 and Bellcore TR-TSY-000194 (ANSI) procedures for
collection and monitoring of network TABS Maintenance Messages or Performance Report
Messages provided by the Central Office, with time-stamped 24-Hour Performance Report
statistics stored in non-volatile memory.
•
Provides independent user and network register sets for TABS performance data — the user set
is unaffected when the Central Office clears the network set.
•
Provides T1-, DS0-, and channel-level diagnostics for extensive diagnostic capabilities.
Fractional T1 Capabilities
The DS1 signal on a T1 line consists of 24 DS0 channels. The SC 553 DSU can be configured to
map user data into either consecutive or alternate DS0s to provide rates from 56 Kbps (1 DS0) to
1.536 Mbps (24 DS0s at 64 Kbps each). Rates that use less than the full 1.536 Mbps are referred to
as Fractional T1 (FT1).
The output rates available from the DSU are multiples of 56 and 64 Kbps because each of the 24
DS0s that make up the T1 line provides a data rate of 56 or 64 Kbps depending on the form of line
coding being used. The DSU can be configured to start a group of DS0s on any DS0 in the T1 line.
The full T1 bandwidth is available when consecutive DS0s are used, but restrictions on ones density
may limit the actual usable bandwidth. Use of consecutive DS0s for N x 64 kbps requires either
B8ZS coding on the network line or provisioning in the DTE to guarantee mark density
requirements.
Using alternate DS0s reduces the T1 bandwidth available for user data by one-half, but it eliminates
restrictions on the content of user data. When the DSU is configured to use alternate DS0s it
maintains minimum ones density at 50% by filling the unused DS0s with ones.
Management
As an SNMP controlled device, the SC 553 DSU can receive commands to set its configuration and
control its functions in the form of entries in its Management Information Base (MIB) tables. SNMP
interface functions between the DSU and its SNMP controller are the responsibility of a
SpectraComm Manager (SCM) card installed in the same SpectraComm Shelf (or pair of shelves)
that holds the DSU.
The SCM card stores and administers MIBs for compatible GDC products in its SpectraComm
Shelf. The SCM card communicates with an SNMP controller, and passes commands and re-
sponses between the controller and the DSU.
In addition to the SC 553 DSU, SCM-compatible products include the SC 521 DSU, GDC V.F 28.8
and Dual V.34 modems, and the data set emulators and line terminating units in the GDC
SpectraComm 5000 system. The SC 553 DSU can be installed in a shelf that holds other types of
SCM-compatible products, with a single SCM used for the control of all the devices in the shelf.
Diagnostic testing performed through SNMP does not require intervention by personnel at remote
sites.
076R155-000
Issue 7
SpectraComm 553 Fractional T1 DSU
Installation and Operation Manual
Fractional T1 Capabilities
1-3
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